1. Field of the Invention
The present invention relates to a secondary battery and, more particularly, to a secondary battery capable of fastening a positive electrode tab and a negative electrode tab to either a cap plate or an external terminal without welding.
2. Description of the Related Art
Recently, as portable electronic apparatuses are being rapidly made small and light, research for secondary batteries to be used as a driving power source has increased. Nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries, and lithium secondary batteries are all used as secondary batteries.
Among the above batteries, the lithium secondary battery may be rechargeable, and may be made small while providing a large capacity. Since the lithium secondary battery has a high driving voltage and a high energy density per specific weight, the lithium secondary battery is widely used in the high-technology electronic apparatus fields. The lithium secondary battery is formed by accommodating an electrode assembly constructed with a positive electrode plate, a negative electrode plate and a separator interposed between the positive electrode plate and the negative electrode plate, in a can together with an electrolyte, and by sealing the upper end of the can with a cap assembly.
The electrode assembly is formed by winding the positive electrode plate, the negative electrode plate, and the separator interposed between the positive electrode plate and the negative electrode plate. A positive electrode tab is coupled to the positive electrode plate so as to protrude toward the upper end of the electrode assembly. A negative electrode tab is coupled to the negative electrode plate so as to protrude toward the upper end of the electrode assembly. In the electrode assembly, the positive electrode tab and the negative electrode tab are separated from each other by a predetermined distance, and they are electrically insulated from each other.
The cap assembly includes a cap plate, an insulating plate, a terminal plate, and an electrode terminal. The cap assembly is coupled to an additional insulating case so as to be coupled to the upper end opening of the can and to seal the can.
A groove for the positive electrode tab and a hole for the negative electrode tab are formed in the insulating case. The insulating case is inserted in order to prevent a short circuit between the top of the electrode assembly and the bottom of the cap assembly which are accommodated within the can. In addition, the insulating case prevents a short circuit which could occur whenever the curved negative electrode tab and positive electrode tab contact the internal wall of the can.
In a lithium secondary battery, the positive electrode tab is coupled to the cap plate by welding, the negative electrode tab is coupled to the terminal plate by welding, and the terminal plate is electrically coupled to the electrode terminal via a terminal hole through the cap plate.
However, when the positive electrode tab and the negative electrode tab are coupled to the cap plate and the terminal plate, respectively, during fabrication of the battery, process time increases. In addition, the reliability of a lithium secondary battery is compromised by the occasional poor welding.